This invention relates to a method of controlling a magnetic bubble memory device which operates over a wide range of temperature.
When an adequate bias field is applied vertically to a magnetic thin plate surface such as garnet or orthoferrite having uniaxial magnetic anisotropy, a cylindrical magnetic domain, the so-called magnetic bubble is generated.
Magnetic bubble devices which perform accumulation of information and logical operation by using such magnetic bubbles, are now under development for practical use in the field because such devices are non-volatile, fully solid state, suitable for large capacity and operate at a comparatively high speed.
For magnetic bubble devices, various functions such as generation, transfer, division, expansion, detection and erasure of magnetic bubbles are required. Moreover, required are bias field application means for stably maintaining the magnetic bubbles in the magnetic thin plate and rotating field application means for moving magnetic bubbles within the magnetic thin plate based on the magnetic pattern formed on the magnetic thin plate.
FIG. 1 shows a typical structural example of a magnetic bubble memory chip used for as a magnetic bubble device. The structure shown in this figure is a so-called major/minor loop. In this figure, 1 is the major loop; 2 is the minor loop; 3 is the detector; 4 is the generator; 5 is the replicator; 6 is annihilator; and 7 is the transfer gate. The solid line indicates the magnetic bubble transfer route by the permalloy pattern formed on the magnetic bubble thin plate, while the broken line indicates the conductor pattern consisting of the gold, etc., formed on the thin plate in the same way. The operation of this device is explained below.
A current is applied to the loop conductor pattern forming the generator 4 in such a direction so as to effectively reduce the bias field and, in accordance with the data to be written, in order to generate the magnetic bubble within the loop. The magnetic bubble generated is transferred in the major loop 1 by the drive field which rotates within the surface direction of magnetic thin film and thereby the bubble containing one data segment (as large as one word, for example) is arranged at the corresponding position of each minor loop 2. At this time, a current is applied to the conductor pattern forming the transfer gate 7 and the magnetic bubble data segment on the major loop 1 is sent to the minor loop 2. The magnetic bubble transferred to the minor loops 2 circulates in the minor loops 2 by means of the drive field, thus storing data.
The stored data can be read as follows. Namely, when the desired magnetic bubble data segment stored in the minor loop 2 comes to the position corresponding to the transfer gate 7, a current is applied to the conductor pattern and thereby the magnetic bubble data segment is transferred to the major loop 1. The magnetic bubble data segment transferred to the major loop is sequentially transferred to the replicator 5 by means of the drive field. The replicator 5 divides the sequentially arriving magnetic bubbles into two parts and transfers one to the detector 3 along the permalloy pattern, and the other to the minor loop via the major loop 1. The detector 3 expands the sequentially appearing magnetic bubbles in order to raise the detection efficiency and also detects changes in electrical resistance of the magnetic resistance element induced by the arriving magnetic bubbles, as changes in voltage. In case it is required to erase the data after reading it and to write new data, it is necessary after dividing the magnetic bubble, to have the annihilator 6 erase the magnetic bubble on the major loop and then send another new data by means of generator 4.
FIG. 2 shows the structure of a package accommodating the magnetic bubble chip shown in FIG. 1. In this figure, 8 is the magnetic bubble chip; 9 is the chip mounting plane; 10 is the XY coil for drive field generation; 11 is the ferrite yoke; 12 is the thin plate magnet for applying bias field; and 13 is the shield case. The triangular currents having a phase difference of 90.degree. as shown in FIG. 3 (a) are applied to each coil of the XY coil to generate the drive field and the square locus of the rotating field as shown in FIG. 3 (b). Such a drive method using the triangular waves has various merits as compared with the drive method using the sine wave. Namely, the circuit structure is simplified, fewer parts are used, a high drive voltage is not required, and integration can be realized easily.
The storing operation of the magnetic bubble memory explained above is stable within the operating temperature range specified by the temperature characteristic of magnetic domain crystal in the magnetic thin film, but such range can be as narrow as 0.degree. C. to +55.degree. C. However, it is required to widen the temperature range up to -20.degree. C. to +55.degree. C. To achieve this range, the devices which satisfy the temperature range are selected from many devices.
Therefore, the step of selection is necessary in order to obtain the devices having the wider temperature range, thus degrading the yield.